Method for molding composite metal-elastomer wheels

ABSTRACT

Method for molding a composite metal-elastomer styled wheel in which a middle mold part consists of a metal wheel disc and rim subassembly. A base mold part seats against the outboard face of the metal wheel in the closed condition of the mold and has a mold cavity surface to provide an ornamental configuration for the outboard face of the plastic body of the composite wheel. There is a clamp which includes a funnel adapted for registry with a liquid reaction mixture injection nozzle coupled with injecting mixing apparatus. The funnel has a nozzle passage registering with a pour opening in the disc in the closed condition of the mold. A sprue pin is affixed to the base mold part in juxtaposed relation to the disc pour opening and cooperates with the margin of the pour opening to define a restricted access opening to the mold cavity during the injection pour of the urethane reaction mixture. The sprue pin is operable to restrict back-flow of the reaction material during gelation of the same in the cure cycle. The sprue pin and disc in the vicinity of the pour opening define a zone of weakness in the cured urethane reaction mixture operable to induce fracture in the zone upon separation of the base mold part from the middle part to thereby cause cleavage of the urethane reaction material adjacent the inboard surface of the middle mold part.

This is a division of co-pending application Ser. No. 015,165 filed onFeb. 17,1987, now U.S. Pat. No. 4,786,027.

This invention relates to wheels for vehicles of the compositemetal-elastomer styled automotive-type with a three-dimensional deeplycontoured ornamental outboard face, and more particularly to moldingapparatus and method for constructing such a wheel.

In the early 1970's Motor Wheel Corporation of Lansing, Mich., assigneeof applicant herein, as well as its then parent company, The GoodyearTire & Rubber Company of Akron, Ohio, developed and introduced animproved form of composite metal-elastomer styled wheel marketed underthe registered trademark "POLYCAST". Such styled wheels provided anautomotive type wheel in which metallic parts of simple, conventionalconfiguration, for which manufacturing equipment was already available,are utilized as the basic structural components to thereby obtain a highstrength standardized wheel construction at minimum cost. Theaesthetically pleasing appearance was imparted to this standard steelbackbone by a permanently adhered ornamental plastic body, either moldedseparately or in-situ as a homogeneous one-piece body or in the form ofa plastic cover secured by an adhesive foam body to the outboard side ofthe wheel. This provided an improved anti-noise characteristic to thewheel and enabled the appearance of the wheel to be readily andeconomically varied to suit different customer's styling requirementswithout varying the basic structural components of the wheel. Additionalbenefits resided in the side impact cushioning to prevent damage to thewheel while retaining the high strength and impact resistance advantagesof the time-proven conventional ductile steel wheel components. Widervariations in styling and contour configurations were also obtained thanwere possible in the previous deep drawn styled all-steel wheels.

Various embodiments of such "POLYCAST" wheels, as well as methods andapparatus for producing the same, are set forth in the following UnitedStates Patents assigned either to the assignee herein or its parent, TheGoodyear Tire & Rubber Company, which are incorporated herein byreference:

    ______________________________________                                        No. 3,669,501   6/1972      Derleth                                           No. 3,756,658   9/1973      Adams                                             No. 3,762,677   10/1973     Adams                                             No. 3,815,200   6/1974      Adams                                             No. 3,918,762   11/1975     Hampshire                                         No. 3,794,529   2/1974      Thompson                                          No. 3,935,291   1/1976      Jackson                                           No. 3,956,451   5/1976      Adams                                             No. 4,398,770   8/1983      Smith                                             ______________________________________                                    

Other prior art patents issued to unrelated parties and directed tovarious facets of such styled composite metal and plastic wheels includeU.S. Pat. Nos. 3,823,982 and 3,998,494 as well as British Patent1,290,946 (1972).

In one embodiment of the manufacture of such POLYCAST wheels, a portionof the mold comprises a conventional metal vehicle wheel having a dropcenter rim secured to a central disc or body having the usual boltcircle holes and a central aperture so that the disc can be mounted onan axle, drum or disc brake assembly. The metal wheel is employed inconjunction with an upper back-up clamp and lower mold part to definetherewith a sealed cavity for molding and attaching a three-dimensionalcontoured plastic overlay, the overlay thus being molded in-situ andpermanently attached to the outboard side of the wheel in the moldapparatus. Preferably, the wheel forms the upper surface of the moldcavity and a reaction mixture of a urethane elastomer liquid adhesivematerial is injected or poured into the mold to fill the cavity andcontact the outboard surface of the wheel assembly. The urethanematerial solidifies to form a high density non-cellular elastomer bodywhich permanently adheres to the outboard surface of the wheelsubassembly. The plastic overlay may also be constructed from a lowerdensity microcellular closed cell urethane elastomer adhesive material.The urethane material is allowed to solidify in the mold cavity and thenthe mold is opened so that the wheel with the overlay securely adheredto it may be removed from the mold. The overlay may then be painted orotherwise covered with a decorative coating to provide a finishedmetallic-appearing ornamental wheel. The urethane elastomer thus forms aplastic body having a three-dimensional contour which is permanentlyattached to the outboard side of the wheel to provide a decorativesurface, and the elastomer overlay appears to be an integral portion ofthe metal wheel.

Hitherto, it has been customary in the commercial practice of moldingthe aforementioned "POLYCAST" wheels to provide in conjunction with theupper mold part a pour nozzle having a funnel-shaped entrance throatleading downwardly into a stem or neck portion having a reduced diametercylindrical gate passage coaxial with the nozzle throat. The stem issurrounded by an annular elastomeric seal which registers and seals withthe margin of a pour opening in the steel disc wheel. During the moldingoperation a special urethane mixing head nozzle is lowered onto the pournozzle throat and the urethane reaction mixture is mixed in the mixingnozzle under relatively high pressure, say on the order of 2,000 poundsper square inch, and injected therefrom into the pour nozzle under aregulated exit pressure of about 50 pounds per square inch to therebyforce the urethane reaction mixture into the mold cavity. At apredetermined time after the mixture has filled the cavity, the mixinghead is retracted.

Once the injected mixture has cooled and cured sufficiently forde-molding, the upper mold part, along with the pour nozzle carriedthereon, is separated from the inboard side of the disc of the wheel byraising the same therefrom. Since the pour nozzle is also filled withthe urethane reaction mixture at the completion of the injection cycle,a solidified riser or sprue is likewise formed therein. Customarily,this excess urethane material will break off, during mold separation oropening, inside the upper end of the nozzle sprue passage at a weaknessplane adjacent the junction of this passage with the funnel throatportion of the nozzle, leaving a cylindrical sprue attached to thecavity urethane material which projects inboard axially from the inboardface of the disc distance on the order of 1 or 11/4 inches. Thus, afterde-molding of the wheel, it has hitherto been necessary to process thesame through a buffing operation in order to remove the projecting sprueor riser from the inboard face of the wheel backbone.

Another related problem occurs because the entrance to the moldingcavity of the wheel mold is open to the sprue and funnel cavities of thepour nozzle. Hence, a substantial amount of "blow back" of the reactionmaterial can occur into these cavities as the urethane reaction materialexpands during cure and gelation is taking place. This blow back canalso cause excessive material to be present on the inboard face of thecast wheel which must be removed, as indicated above, thereby furtheradding to material and processing cost. Moreover, since there is a needto keep the mold cavity "packed" to some extent to obtain the properoverlay body density to produce a good product, excessive blow-back cancause defects due to insufficient packing.

A further problem related to the above occurs in the construction ofcertain styles of POLYCAST wheels wherein the urethane decorative bodyhas a very wide (radially) center opening so that the inner periphery ofthe urethane body material is disposed radially outwardly of and distantfrom the center area of the steel disc. With this "wide-open-center"styling the entire central bolt hole mounting portion and continguousportions of the disc "hat" or crown may thus be devoid of urethane.Accordingly, in these constructions, it is not possible to inject theurethane mixture through a pour hole located in the disc bolt holecircle area. Injection through an alternative disc entrance to the moldcavity is thus needed, while still retaining the same mold back-up clampand pour nozzle construction to reduce manufacturing cost.

Accordingly, an object of the present invention is to provide animproved method of making a composite metal-elastomer wheel constructionof the aforementioned POLYCAST styled wheel type which overcomes theaforesaid problems of excessive sprue risers, eliminates extra finishingsteps, overcomes the aforementioned "blow back" problems, and is usablein producing a wide variety of overlay body designs, including"wide-open-center" types.

Another object is to provide improved mold apparatus for practicing theaforementioned improved method which is economical in construction andreliable in operation.

The invention, together with additional objects as well as features andadvantages thereof, will become apparent from the following detaileddescription and the appended claims taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a fragmentary top-plan view of the inboard side of a metaldisc and rim subassembly employed in the construction of a compositemetal-elastomer styled wheel in accordance with the method and apparatusof the present invention.

FIG. 2 is a vertical cross-sectional view taken on the line 2--2 of FIG.1 but also showing the upper and lower mold parts juxtaposed in assemblyto the disc and rim subassembly and provided with a first embodiment ofa sprue pin in accordance with the present invention.

FIG. 3 is a fragmentary sectional view illustrating the sprue pin andassociated riser pip formed during reaction injection molding of thewheel, this view being enlarged over the corresponding portion of FIG. 2to better illustrate detail.

FIG. 4 is a vertical elevational view of the first embodiment of thesprue pin provided in accordance with the present invention shown byitself.

FIG. 5 is a vertical elevational view of a second embodiment of thesprue pin of the invention shown by itself.

FIG. 6 is a fragmentary vertical sectional view taken on the line 2--2of FIG. 2 but illustrating a third embodiment of a sprue pin inaccordance with the invention.

FIG. 7 is an enlarged vertical part-elevational and part-sectional viewof the sprue pin of FIG. 6 shown by itself.

FIG. 8 is a fragmentary top plan view of a fourth embodiment of moldapparatus provided in accordance with the present invention.

FIG. 9 is a vertical cross-sectional view taken on the like 9--9 of FIG.8.

Referring in more detail to the accompanying drawings, FIGS. 1 through 4illustrate a first embodiment of the improved apparatus for practicingthe improved method of the invention for constructing a compositemetal-elastomer styled wheel of the aforementioned type. The wheel isgenerally designated at 20 and comprises, by way of a preferred example,a conventional drop center steel rim 22, a central steel disc or body 24permanently secured, as by welding, to the rim, prior to the moldingoperation. Wheel 20 also includes an ornamental three-dimensionalcontoured overlay, generally designated at 26 (FIG. 2), secured to theoutboard face of disc 24 and to the outboard surface of rim 22. Disc 24is provided with a circle of bolt holes 28 and a central wheel spindleaperture 30 so that wheel 20 can be removably attached to a wheel huband associated disc brake or drum brake assembly. For decorativepurposes and for brake ventilation, a plurality of cut-outs or ventholes 32 are provided in disc 24 (only five of a circular array of 24such holes being shown in FIG. 1). The particular configuration of thesteel components of wheel 20, including rim 22 and disc 24, may followsolely utilitarian considerations such as strength of the wheel and easeand economy of manufacture, since the aesthetic appearance of the wheelis determined largely by the three-dimensional contour of the ornamentaloverlay 26. The three dimensional contours of overlay 26 in turn aredetermined by the particular ornamental or aesthetic appearance desiredby the designer of wheel 20.

In the ornamental exemplary design of FIGS. 1 and 2, overlay 26 has acentral annular section 34 with a generally smooth frusto-conical outerface 36, and a plurality of fins 38, which radiate outwardly fromsection 34 to an outer annular peripheral portion 40. Pockets 42 areprovided between each adjacent pair of fins 38 which extend axiallyinboard to provide a urethane aperture 44 within each disc aperture 32.Section 34 of overlay 26 has an internal, slightly frusto-conical wall50 diverging outboard axially of the wheel and terminating at an axiallyinset hub cap seating surface 52. Wall 50 defines a relatively largecavity in the center of overlay 26 and is adapted to receive the vehiclewheel spindle therein in a mounted condition of wheel 20.

FIGS. 2-4 also illustrate an improved molding apparatus, and improvedmethod of making wheel 20 utilizing such apparatus, in accordance withthe invention, which incorporate many of the features of the moldingapparatus and method illustrated in conjunction with FIGS. 7 through 11of the aforementioned Adams U.S. Pat. No. 3,762,677, which isincorporated herein by reference. Likewise, the molding apparatus ormold 200 described in columns 11-16 of the '677 patent is incorporatedherein by reference, and identical reference numerals are employed inFIGS. 2 and 3 to identify elements alike in structure and/or function.

Mold apparatus 200 thus comprises the three main components: namely, alower mold part 202 (FIG. 2), the metal wheel subassembly 22-24, and anupper mold half 206 which serves as a backup support for clamping wheel22-24 onto mold part 202. Lower mold part 202 has an annular lip in theform of a resilient seal 224 adapted to seat against an annular portionof the outboard face of rim 22. Mold part 202 also has a surface 230 onits upper side radially inwardly of seal 224 adapted to define, with theoutboard face of wheel subassembly 22-24, a mold cavity in which thedecorative plastic overlay 26 is cast, the same being suitably contouredto provide the ornamental configuration to form the outboard decorativeface 36, 38 of wheel 20.

To assemble mold 200, wheel subassembly 22-24 is placed against lowerpart 202 as shown in FIG. 2 with the outboard tire bead-retaining flange226 of rim 22 resting on or in light contact with seal 224. This alsolightly seats the bolt circle portion 214 of disc 24 against an annularinner seal 234 mounted on the upper face of a mold pedestal 235 which inturn is seated on the center of face 230 of mold part 202 and removablysecured thereto by a stud 233. Pedestal 235 provides a core to form thewall 50 defining the wheel well cavity in the center of overlay 26. Seal234 is adapted to seal the mold cavity around its inboard innerperimeter in the fully seated condition of wheel subassembly 22-24 onmold part 202.

Upper mold part 206 has two pairs of upright posts 300. These posts inturn are fastened to a suitable molding press ram for raising andlowering of upper mold part 206 as will be well understood in the art.This apparatus is used to urge upper mold part 206 downwardly againstwheel subassembly 22-24 as shown in FIG. 2 to clamp mold 200 in itsfully closed position.

Mold part 206 has a resilient annular pad 236 having a configuration onits underside adapted to seat against the inboard face of disc 24 inoverlying relation to disc vents 32 and associated core protrusions 238of lower mold part 202 to thereby force the disc-rim subassembly 22-24further toward part 202 and then retain parts 202 and 22-24 in sealingengagement. A steel funnel 312 is secured by bolts 313 onto the uppersurface of clamp plate 244 and has a coaxial neck 314 which extendsdownwardly through a washer seal 316 disposed within seal 237, the lowerend face 317 of neck 314 being disposed slightly above or in recessedrelation to the lower end face 318 of washer seal 316. Disc 22 isprovided with a pour opening 290 between a pair of adjacent bolt holes28 therein. Neck 314 of funnel 312 and washer seal 316 are positionedfor coaxial registry with pour opening 290, and the lower face 318 ofseal 316 seats in sealed relation on the inboard face of disc 22 aroundthe margin of opening 290. Pedestal 235 has a notch 288 (indicated inphantom by dash lines in FIG. 1) in its upper surface which registerswith pour opening 290 and funnel neck 314 to serve as a sprue fordirecting the liquid urethane reaction mixture into the mold cavityduring pouring of the mold.

Lower mold part 202 has a locating pin 250 affixed to and protrudingupwardly from pedestal 235 parallel to the wheel axis which protrudesthrough an associated one of the disc bolt holes 228 in the closedcondition of the mold for angularly locating the rim disc subassembly22-24 accurately on the lower mold part 202. Upper mold part 206 has acentral locating core 252 projecting through the disc center opening 30and into the space below disc 24, core 252 having a close clearance fitwith disc center hole 30 to thereby center the metal wheel subassembly22-24 relative to the upper mold part 206 in the closed condition of themold 200.

Funnel 312 has a conical throat portion 320 downwardly convergent andcommunicating with a coaxial cylindrical neck passage 322 which opens atits lower end at face 317 of neck 314. In accordance with the principalfeature of the present invention, instead of the previous unrestrictedcommunication of passage 322 via a circular disc opening with the spruenotch passage 288 in pedestal 235, a predetermined annular orifice isprovided in the form of a sprue pin 330 (FIGS. 2, 3 and 4) interposed indisc pour opening 290. Pin 330 has an extending threaded mounting shank332, a cylindrical mid-portion or body 334 and a tapering, bullet shapednose 336. Sprue pin 330 is mounted on pedestal 235 by screwing pin 332into a threaded socket located in the bottom wall of the spruepassageway 288, as best seen in FIG. 2. The length and diameter of pinbody 334 is sized to position the radially extending upper surface 338of the body within the disc pore opening 290 between the planes of theinboard and outboard surfaces of the disc 24. Pin 330 is coaxiallyaligned with opening 290 as well as funnel neck passage 322.

As best seen in the enlarged view of FIG. 3, the outer surface of pinbody 334 and the inner cylindrical wall of pore opening 290 define anannular passageway 340 therebetween having a given flow controllingcross-sectional area. Similarly, the surface of pin nose 336 isdimensioned to have its tip protrude slightly upwardly into the outletend of funnel passage 322 so as to define therebetween another annularpassageway 342. The predetermined clearances 340 and 342 are selected tocause a flow restriction for the incoming liquid urethane reactionmixture during filling of the mold cavity which does not prolong theprevious two-second fill time for the mixture to enter and fill the moldcavity, taking into consideration the viscosity of the mixture and theavailable injection pressures. To this end the small annular orifices340 and 342 are designed to be of the same cross-sectional area normallyprovided with the prior open circle pour opening in the disc.

However, as contrasted to such prior circular pour hole, these annularorifices have a small radial dimension between their inner and outerconcentric surfaces. Hence, once the mold cavity becomes substantiallyfilled, and the urethane reaction mixture starts to cure such thatgelation takes place, the solidifying particles of urethane tend toblock reverse flow through these narrower annular orifices to therebyprevent reverse flow and escape of the urethane from the mold cavity.Hence the sprue pin of the present invention helps overcome the previous"blow-back" problem of a circular pore opening, which has previouslyposed difficulty, in two respects: (1) it reduces or eliminates theexcess material previously present on the inboard face of the cast wheelwhich heretofore had to subsequently be removed in a finishingoperation, thereby reducing material and processing costs; and (2) therestriction to back flow keeps the mold cavity "packed" to some extentin order to obtain the proper density to produce a good product, whereasexcessive blow-back can cause a weakness in this respect. Moreover, byutilizing sprue pin 330 the injection nozzle of the mixing head can beremoved from funnel 312 at an earlier point in the processing cycle,permitting the mold assembly to be transferred from the fill station toa cure station and replaced with another empty mold assembly in a fastersequence, thereby increasing production efficiency.

After the injection filled mold assembly has been allowed a sufficienttime to complete the cure of the urethane reaction mixture forming theornamental overlay 26, mold 200 is opened by raising upper mold half 206to separate the same from disc and rim subassembly 22-24. Before thisoccurs, it will be noted that a riser of solidified and cured urethanereaction material will have formed in the funnel neck passage 322 andfunnel throat 320. This riser is best illustrated in FIG. 3 and consistsof a stem 350 and a conical head 352 (funnel 312 being omitted forclarity). With the prior mold apparatus utilizing an unrestrictedcircular pour opening, during the initial upward motion of upper moldclamp 206 the riser would, under the stretching stress of moldseparation, fracture at a point of weakness generally indicated by thedash line 354 in FIG. 3, close to the junction of stem 350 with head352. The severed portion of stem 350 remaining attached to the main bodyof the urethane material 26 via disc opening 290 thus represented aprojection of scrap material which had to be removed in a subsequentfinishing operation.

However, with the provision of sprue 330 of the invention, the annularorifices 340 and 342 create two planes of weakness in the urethanematerial respectively within and adjacent the disc opening 290.Accordingly, upon initial raising of upper mold half 206, fracture ortear separation of stem 350 from the main body 226 of urethane materialwill occur either within opening 290, slightly thereabove, or in a zonebetween these two planes of weakness. Hence, removal of upper mold half206 will result in separation of the waste material 350 and 352 at ornear the inboard face of disc 24, thereby materially reducing oreliminating the need for a subsequent finishing operation. The separatedriser 350, 352 is cleared from funnel 312 by forcing the same upwardlytherefrom in the manner as substantially heretofore performed, thusadding no further complications to processing. When the disc and rimsubassembly 22-24, with the ornamental plastic body 26 adhered thereto,is separated from the lower mold part 202, sprue pin 330 will bewithdrawn from body 26, leaving a complemental cavity in the outboardface of body 26. However this cavity is located radially within thecenter cavity of body 26 defined by mold pedestal 235 and hence will notbe visible in use because this central area of the wheel assembly istypically covered by an ornamental hub cap or the like detachablymounted to overlay 26.

Referring to FIG. 5, a second embodiment of a sprue pin 360 isillustrated by itself, pin 360 being provided with the same nose 336 andthreaded shank 332 as pin 330. However the central body portion 362 ofpin 360 is substantially reduced in diameter relative to body 334 inorder to adapt sprue pin 360 to a disc pour opening having acorrespondingly reduced inside diameter. Such variations in thediameters of disc pour openings occasionally occur in the constructionof "POLYCAST" wheels as may be necessary to accommodate different wheeldesigns. In any event, it will be understood that the diameter of bodyportion 362 is selected relative to the inside diameter of the disc pouropening to define the annular restriction 340 there between, whereas thedimension of pin nose 336 need not be altered to define the annularrestriction 342 because the same size funnel 312 is used in allapplications.

A third embodiment of a sprue pin and associated mold apparatus inaccordance with the present invention is illustrated in FIGS. 6 and 7.In this embodiment a modified sprue pin 370 is provided which mounts inthe mold apparatus 200 in the same manner as sprue pin 330. Sprue pin370 thus comprises a fillister head screw 372 having a threaded shank374 which screws into the threaded socket in pedestal 235, and a conicalhead 376 provided with a screw driver cross slot 378. A steel washer 380is received on shank 374 so as to abut head 376. Washer 380, a portionof screw shank 374 and screw head 376 are encapsulated in an annularbody 382 made of a suitable elastomeric material, such as siliconerubber, to form a permanent assembly. The upper surface 384 of screwhead 376 is slightly recessed relative to the upper surface 386 of body382. Preferably body 382 has a conical throat 388 complimentary to screwhead 376 and extending therebeyond to a junction with surface 386 suchthat the upper edge of body 382 defines a narrow annular flexible lip.

Pin 370 is dimensioned such that when installed on pedestal 235 as shownin FIG. 6, the upper surface 386 of the silicon rubber head 382 in itsrelaxed free state condition is positioned within a tolerance rangedefined by a slight clearance with the outboard face (underside) of disc24 to a contacting, slightly compressed sealing condition therewith,depending upon the tolerance ranges and build-up of the various partsemployed to construct mold assembly 200. Due to the soft, pliable natureof the silicone rubber of body 382, head 382 cannot be damaged whenplacing the rim-disc 22-24 subassembly onto the lower mold part 202. Thelip 386 of body 382 will either touch or come very close to the outboardface of disc 24 in the fully closed condition of mold upper half orclamp 206. The outside diameter of head 382 is made slightly larger thanthe inside diameter of the disc opening 290 so as to radially overlapthe margin of opening 290.

Regardless of whether upper lip 386 of body 382 is touching the discmetal around opening 290, or spaced with a very slight clearancetherefrom, when the liquid reaction mixture is injected via funnel 312into and through pour opening 290, the silicone rubber material of head382 is soft enough so that the lip area 386 of the head will deflectunder the flow injection pressure, thereby allowing the reaction mixtureto flow into the mold cavity at a satisfactory rate. Although pin 370thus may define in a non-pour condition a closed passageway or a muchmore restricted annular orifice than is the case with pin 330,nevertheless in its deflected condition in the injection pour state thesame does define an adequately open annular restricted passage betweenlip 386 and the juxtaposed outboard face of disc 24 around the margin ofopening 290. Pin 370 thus does cause a slight increase in back pressureas compared to pin 330, but it has been found that this slight increasein back pressure improves the mixing of the initial flow of reactioninjection material from mixing head. After the pour has been completed,the resilience of the material of head 382 causes the same to return toits normal free state condition, either contacting or slightly spacedfrom the disc. It also has been found that back flow of the reactionmixture is prevented in a manner similar to, but improved over, theresults obtained with pin 330. Moreover, utilizing the modified spruepin 370 creates a thin section weakness fracture zone in the solidifiedurethane material in the vicinity of the lip 386 which causes riser 350to break off at this point upon raising of upper mold half 206 from thedisc-rim subassembly 22-24. Hence, no excess cured material protrudesfrom the inboard side of the disc, thereby again eliminating asubsequent scrap removal operation.

Another advantage of the modified sprue pin 370 relative to sprue pin330 has been found to result when the same is used with a thin-film moldrelease sheet. It has been customary hitherto in commercial use of priorart "POLYCAST" molds to place a sheet of polyethylene film between theinboard side of disc 24 and the undersurface of mold clamp 206. Thisfilm acts like a mold release compound and also protects the rubber lidsealing component 236. The film is clamped between lid 206 and disc 24(and the projections 238 of the lower mold part 202) and hence initiallyforms an imperforate barrier across the pour opening 290. However, whenthe reaction mixture is forced under the high injection pressure fromthe injection nozzles through funnel 312, the pressurized liquidmaterial will puncture the polyethylene film, creating a small holecoaxial with pin 370 in the space immediately above the surface 384 ofthe screw head 376. The material thus flows through the film andradially outwardly over the deflected lip 386 of the silicon body 382during pouring. Pin 370 functions in conjunction with this film to tendto hold the film in position during and after the pour so that the filmitself also provides a natural weak point in the sprue stem 350 in thevicinity of the pour opening 290. By contrast, use of this polyethylenefilm with pin 330 has been found to produce a break which generates aflap in the film which tends to be pushed aside during the flowinjection and does not return to its original position. Although thisdoes not interfere with the aforementioned operation and improvedresults of sprue pin 330, the additional advantage of having the filmproduce a natural weak point in the sprue stem, as occurs with sprue pin370, is not obtained with pin 330.

Referring to FIGS. 8 and 9, a fourth embodiment of mold apparatus andmethod in accordance with the invention is illustrated wherein thestructure previously described is given like reference numerals, andstructure similar in function and operation to that previously describedis given a like reference numeral raised by a prime suffix. In thisembodiment, the mold apparatus is modified to construct a so-called"wide-open-center" "POLYCAST" wheel design. Accordingly, lower mold part202' is provided with an annular seal 400 adapted to seat against thecrown of the hat section of disc 24 so that the mold cavity for theornamental body 26' is disposed radially outwardly of seal 400, andextends out to the outer seal 224. Hence, with this design, a pouropening in the bolt circle region of the disc cannot be employed.Instead, in accordance with this embodiment of the invention, one of thevent holes 32' in the disc is employed as a radially remote pour openingfor the mold cavity. A modified vent sealing pad 236' is provided on theupper mold part 206' which has a radially inwardly protruding arm 402which extends radially inwardly over the inboard surface of disc 24 tosurround a shortened nozzle 314' of the funnel 312'. Arm 402 has arunner channel 406 which communicates with nozzle passage 322' at itsradially inner end, and extends along the inboard side of the disc,following the contour of the same, to a radially outer terminal portionwhich surrounds the disc valve opening 32'.

A modified core protrusion 238' is provided in conjunction with theselected disc vent-pour opening 32'. Protrusion 238' has a free endportion 410 which protrudes axially of the wheel assembly in an inboarddirection through the disc opening 32', and is contoured on its upperedge to seat against the surface of runner channel 406 in the assembledcondition of the mold. The side walls of protrusion 410 are contouredcomplimentarily to the side walls of the disc valve opening 32' todefine therebetween an annular (generally rectangular) orifice openingwhich communicates with the radially outboard end of runner channel 406and the mold cavity space in which body 26' is to be formed. Protrusion410 thus is designed to function similar to core pin 330 to permitadequate in-flow of urethane reaction material into the mold cavityduring the injection pour cycle, but to limit back-flow therefrom asgellation takes place. Upon separation of mold lid 206' from the rim anddisc subassembly 22-24 the solidified urethane material occupying therunner passage 406 tends to cling to the pad 402 and to separate fromdisc 24. As this takes place, the weakened fracture line generated inthe annular space between protrusion 410 and disc vent opening 32' willcause separation of the urethane material to occur in this weaknessplane. Upon separation of the lower mold part 202' from the finishedwheel, the urethane pocket 44' will remain as in the first embodiment.

By way of illustration and not by way of limitation, the followingspecifications have been found to provide successful performance andachievement of the objects of the invention in working examples of thepresent invention:

Sprue Pin 330

Internal diameter of disc pour opening 290--0.500"

Outside diameter of body 334--0.437",

Base diameter of nose 336--250"

Axial length of nose 336--0.187"

Minimum radial distance between body 334 and inner periphery of opening290--0.032"

Minimum radial distance between nose 336 and inner surface of passage322--0.062"

Approximate injection pressure of liquid urethane reaction mixtureentering funnel 312--Approx. 2000 p.s.i.

Inside diameter of passage 322--0.250"

Sprue Pin 370:

Diameter of body 382--0.625"

Axial length of body 382--0.4375"

Distance between screw head surface 384 and body lip surface 386--0.062"

Radial width of lip 386--0.03125"

Diameter of pour opening 290 for pin 370--0.313"

From the foregoing description, it will now be apparent that the presentinvention provides an improved mold apparatus and method forconstructing "POLYCAST" composite metal and elastomer styled wheelswhich satisfies the aforementioned objects, resulting in reducedprocessing and material costs without thereby increasing the timerequired to injection fill the mold cavity. It is also to be understoodthat, although the foregoing description and drawings describe andillustrate in detail various successful working embodiments of thepresent invention, to those skilled in the art to which the presentinvention relates, the present disclosure will suggest manymodifications and constructions as well as widely different embodimentsand applications without thereby departing from the spirit and scope ofthe invention. The present invention, therefore, is intended to belimited only by the scope of the appended claims and the applicableprior art.

I claim:
 1. A method for molding a composite styled wheel of the typecomprising a metal part consisting of a metal disc and rim subassemblyoperable as metal street wheel when a pneumatic tire is mounted on saidrim, and a decorative urethane plastic body permanently molded to themetal part at the outboard face thereof, utilizing molding apparatuscomprising a base mold part configured to receive said metal wheel partthereagainst and having an annular lip adapted for sealing engagementagainst an annular portion of the outboard face of the metal wheel partradially outwardly of the center of the disc in the closed condition ofsaid molding apparatus, the base mold part having a mold cavity surfaceto provide an ornamental configuration for the outboard face of theplastic body of the composite wheel, the mold cavity surface in the moldclosed condition defining with at least part of the outboard face of themetal wheel part a mold cavity axially adjacent the outboard face of themetal wheel part, a clamp adapted to seat in the mold closed conditionagainst the inboard face of the metal wheel part at least adjacent theouter perimeter of the disc for urging the metal wheel part into sealingengagement with the base mold part, the mold parts being axiallyseparable from one another to open the molding apparatus and at clearsaid metal wheel part from the clamp and base mold parts, funnel meansadapted for registry with a liquid urethane reaction mixture injectionnozzle coupled with injection mixing apparatus, the funnel means havinga nozzle passage registering with the inboard side of a pour opening inthe disc in the closed condition of the mold, and sprue pin meansaffixed to the base mold part in juxtaposed relation to the disc pouropening, the sprue pin means being adapted to cooperate with the dicspour opening to define a restricted annular access opening to the moldcavity during the injection pour of the urethane reaction mixture, thesprue pin means being operable to restrict back-flow of the reactionmaterial via the pour opening during gelation of the same in the curecycle, the sprue pin means being adapted to cooperate with the disc inthe vicinity if said pour opening to define a zone of weakness in thecured urethane reaction mixture operable to induce fracture in theweakness zone upon separation of the clamp funnel means from the metalpart to thereby cause cleavage of the urethane reaction materialadjacent the inboard surface of the metal part, wherein the wheel ismolded pursuant to the following steps:(1) said middle wheel mold partis seated and located on said base mold part with the inboard side ofsaid disc of said middle metal mold part exposed for access thereto, (2)a thin film mold release plastic in sheet form is next placed so as tooverlie the inboard side of said disc of said middle metal mold part soas to cover said inboard side at least over and around the pour openingin said disc. (3) said clamp is seated in closed condition against theinboard face of said middle metal wheel mold part to urge said moldparts to closed condition with said thin film sheet clamped between saidmiddle metal wheel mold part and said clamp, (4) said urethane reactionmixture in liquid form is injected via said funnel means under injectionpressure to thereby rupture said thin film juxtaposed to said restrictedaccess opening and thence flow into the mold cavity to fill the same,and (5) said urethane reaction mixture is allowed to cure sufficientlyin said mold to permit demolding by separation of said mold partswhereby cleavage of the urethane reaction material occurs in thevicinity of the rupture zone in said thin film sheet.
 2. The method asset forth in claim 1 wherein the sprue pin means utilized in said methodcomprises a cylindrical body made of soft flexible material, said bodyhaving a face juxtaposed to the outboard side of said disc of saidmiddle mold part in the closed condition of said mold to contact orprovide slight clearance therebetween in the free state condition ofsaid body, the periphery of said body being exposed to and disposedwithin the mold cavity or a gate passageway leading thereto.
 3. Themethod as set forth in claim 1 wherein said thin film sheet is utilizedto cover substantially all of said inboard side of said disc.
 4. Themethod as set forth in claim 2 wherein said soft flexible material issilicon rubber.